graph valid tree solution

Author: yhkee0404

graph-valid-tree/yhkee0404.kt

@@ -0,0 +1,48 @@
+class Solution {
+    /**
+     * @param n: An integer
+     * @param edges: a list of undirected edges
+     * @return: true if it's a valid tree, or false
+     */
+    fun validTree(n: Int, edges: Array<IntArray>): Boolean {
+        // write your code here
+        val adj = List(n) {mutableListOf<Int>()} // S(V, E) = O(V + E)
+        edges.forEach {
+                    adj[it[0]].add(it[1])
+                    adj[it[1]].add(it[0])
+                }
+        var t = 0
+        val tortoiseStack = mutableListOf<MutableList<Int>>(mutableListOf(0, 0, -1))
+        val hareStack = mutableListOf<MutableList<Int>>(mutableListOf(0, 0, -1))
+        var tortoise = listOf(-1)
+        while (! hareStack.isEmpty()) { // T(V, E) = O(V + E)
+            val hare = hareStack.last()
+            if (hare[1] == adj[hare[0]].size) {
+                hareStack.removeLast()
+            } else if (adj[hare[0]][hare[1]] != hare[2]) {
+                hareStack.add(mutableListOf(adj[hare[0]][hare[1]], 0, hare[0]))
+            }
+            if (hare[1]++ != 0) {
+                continue
+            }
+            if ((t++ and 1) == 1) {
+                while (! tortoiseStack.isEmpty()) {
+                    tortoise = tortoiseStack.last()
+                    if (tortoise[1] == adj[tortoise[0]].size) {
+                        tortoiseStack.removeLast()
+                    } else if (adj[tortoise[0]][tortoise[1]] != tortoise[2]) {
+                        tortoiseStack.add(mutableListOf(adj[tortoise[0]][tortoise[1]], 0, tortoise[0]))
+                    }
+                    if (tortoise[1]++ != 0) {
+                        continue
+                    }
+                    break
+                }
+            }
+            if (hare[0] == tortoise[0]) {
+                return false
+            }
+        }
+        return t == n
+    }
+}